Detecting lightning with sensor

Anyone have any ideas on detecting lightning using a light (or some other) sensor I could hook up to an Arduino?

I have vague ideas of using a photodetector of some sort to trigger some behaviour. It sounds like a hard thing to calibrate.

I know most commercial strike detectors use a radio/magnet detector, but I just need to know when there is a distant flash in an otherwise dim location.

Anyone else done this? I'm probably reinventing the wheel, I know.

Feel free to tell me that my approach is FOS. I'm of to the local 'lectronics shop tomorrow and I'm going to pick up an assortment of stuff that I think might work. Anything I should add to the list?

D'oh. Just found Hobby Robotics » Triggering a Camera’s Flash with Sound and Light

I thought I'd checked the Playground. Bad developer. No doughnut.

Feel free to add hints or horror stories.

(and this)
http://www.glacialwanderer.com/hobbyrobotics/?p=16